Throttle body

ABSTRACT

A lightweight, low cost throttle body and throttle valve placed in the body, both formed of resins, that resolve the problem of excessively large gap formation is disclosed. Circumferentially oriented filler contained in a resin forming a throttle valve compensates to make the radial linear expansion coefficient of the throttle valve substantially equal to that of a bore. Grooves are formed on concentric circles in the throttle valve to orient filler circumferentially. A throttle valve provided with circumferentially oriented filler can be formed by impregnating an aggregate formed by circumferentially arranging the filler with a resin and curing the resin. A rib is formed in a part near a throttle shaft to control molding shrinkage so that the roundness of the bore is small.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a throttle valve made of resin used ina throttle body made of resin. Research and development activities havereduced the weight of automobiles to reduce fuel consumption. Aconventional throttle body, one of the components of an intake system,is manufactured by aluminum die casting. Efforts have been made inrecent years to provide lightweight, low-cost throttle bodies by formingthrottle bodies of resins.

[0002] This invention relates to a throttle valve made of resin used ina throttle body made of resin. Research and development activities havereduced the weight of automobiles to reduce fuel consumption. Aconventional throttle body, one of the components of an intake system,is manufactured by aluminum die casting. Efforts have been made inrecent years to provide lightweight, low-cost throttle bodies by formingthrottle bodies of resins.

[0003] The bore of a throttle body must be formed so that the gapbetween the bore wall defining the bore of the throttle body and athrottle valve placed in the bore of the throttle body is in the rangeof 80 to 100 μm. The bore of a conventional throttle body formed by diecasting is finished by machining to form the bore to the desiredaccuracy. If a resin throttle body can be formed such that its bore isformed at an accuracy that insures the gap in the aforesaid range,machining is unnecessary. The roundness of the bore after moldingshrinkage, the roundness of the throttle valve (hereinafter, roundnessis used to represent variations in diameter), and errors in the insidediameter of the bore must be equal to those of an aluminum throttlevalve formed by die casting. It is necessary to prevent the interferencebetween the bore wall and the throttle valve, and an excessive increasein the gap between the throttle body and the throttle valve due tothermal deformation caused by the variation of temperature between avery low temperature and a high temperature exceeding 100° C.

[0004] A method of preventing irregular deformation proposed in JP-A No.169473/1998 places a filler in an orientation in a bore part of athrottle body defining a bore. It is thought that the gap can be reducedwhen a metal throttle valve formed by machining is placed in such a borepart.

[0005] For cost reduction, the throttle valve must be formed of resin toomit a machining process. When both a throttle body having a bore and athrottle valve to be placed in the bore are formed of resins, thethrottle body and the throttle valve can be formed of different resinshaving similar coefficients of expansion. Hence the initial gap betweenthe bore wall and the throttle valve can be substantially maintained.When the throttle valve is formed of a resin having a thermalconductivity lower than those of metals, it is possible to preventfreezing that occurs in metal throttle valves during operation. Even ifboth the throttle body and the throttle valve are formed of the sameresin containing the same amount of filler, the throttle body and thethrottle valve will have different coefficients of linear expansion, anddeform by different amounts due to the difference between the throttlebody and the throttle valve in the orientation of the filler.Consequently, there is the possibility that the throttle valve willinterfere with the bore wall, and thus the gap between the bore wall andthe throttle valve increases.

[0006] Recent internal combustion engine design has tended to reduce theidle throttle valve opening to reduce idle speed. When the idle throttlevalve opening is reduced, the possibility increases that contaminants,such as carbon contained in the recirculated exhaust gas, and oilscontained in the blowby gas, will adhere to the periphery of thethrottle valve. If those contaminants deposited on the throttle valveare solidified by the heat of the internal combustion engine, thethrottle valve locks to the bore wall and, in the worst case, thethrottle valve will not move even if the accelerator pedal is operated.

BRIEF SUMMARY OF THE INVENTION

[0007] This invention provides a throttle body such that the thermaldeformation of the bore wall of the throttle body is substantially equalto that of a throttle valve at temperatures in the range of a very lowtemperature to a temperature exceeding 100° C. The gap between the borewall and the throttle valve is the same as the gap between the bore wallof a conventional throttle body and a conventional throttle valve, andprovides a low-cost, high-performance throttle body. The invention alsoreduces the roundness of a bore after molding shrinkage and reduces thegap between a throttle valve and the bore. In addition, it prevents thefixation of the throttle valve as sometimes caused by solid depositssuch as carbon and oils.

[0008] To solve the foregoing problems, according to the presentinvention, a filler contained in a resin is oriented in acircumferential direction to make the linear expansion coefficient of athrottle valve in a radial direction approach that of a bore. This makesthe thermal deformation of the throttle valve approach that of the boreto prevent the aforesaid interference and the enlargement of the gap.

[0009] To solve the foregoing problems, a throttle body according to anembodiment of the present invention includes a throttle shaft extendedsubstantially diametrically across an intake cylinder (bore); and athrottle valve fixed to the throttle shaft and contained in the bore,wherein the bore and the throttle valve are made of a resin containingfiller, and the difference between circumferential deformation of thebore and radial deformation of the throttle valve is in the range of 0to 40 μm at temperatures in the range of −40° C. to 120° C. In addition,a throttle body according an embodiment of the present inventionincludes an intake cylinder (bore); and a throttle valve, wherein thethrottle valve and the bore are formed of resins containing filler, thedifference between the linear expansion coefficient of the throttlevalve and that of the bore being in the range of 0 to 4×10⁻⁶/° C.

[0010] Preferably, in the throttle body according to an embodiment ofthe present invention, the fillers in the bore and the throttle valveare oriented in substantially the same direction, or are randomlyoriented in the bore and the throttle valve. In addition, in someembodiments, the throttle valve is provided with circumferential groovesor ribs, and the filler is substantially circumferentially oriented.

[0011] To form the throttle body, the throttle valve is made bysandwiching an aggregate formed by circumferentially arranging thefiller between resin layers. Preferably, the throttle valve is made of aresin different in filler content from that forming the bore to make theradial thermal expansion coefficient of the throttle valve nearly equalto the circumferential linear expansion coefficient of the bore.Furthermore, in the throttle body according to the present invention, atleast a peripheral part of the throttle valve facing the bore wall ofthe bore is made of a resin containing a fluorocarbon resin or is coatedwith a fluorocarbon resin.

[0012] A preferred embodiment of the throttle body according to thepresent invention includes a throttle shaft extended substantiallydiametrically across an intake cylinder (bore); and a throttle valvefixed to the throttle shaft and contained in the bore; wherein the boreis made of a resin, and an annular rib of a fixed or continuouslychanging width, or parts of such an annular rib, are formed in a partcorresponding to the throttle shaft of the bore to counterbalance theeffect of sinks due to bosses. Typically in the throttle body theminimum thickness is ⅔ of maximum thickness or below.

[0013] To solve the foregoing problems, in the throttle body accordingto the present invention, ribs are formed in parts of the bore aroundthe throttle shaft such that the product of maximum height and thicknessis in the range of 15 to 40% of the heights and the mean thickness ofthe bosses and the product of minimum height and thickness is in therange of 20 to 80% of the product of maximum height and thickness. Thebore is provided in a part thereof with a rib capable of limiting theroundness (diameter) of a part of the bore in the range of ±5 mm alongthe center axis of the bore from a position corresponding to thethrottle shaft to 80 μm or below. The ribs are formed in the parts ofthe intake cylinder defining the bore around the throttle shaft toreduce the roundness of the bore after mold shrinkage. The presentinvention also often adds an additive to the resin to suppress theadhesion of carbon and oils to the throttle valve.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a perspective view of a throttle valve in a firstembodiment according to the present invention;

[0015]FIG. 2 is a side elevation of a throttle body;

[0016]FIG. 3 is a plan view of the throttle body;

[0017]FIG. 4 is a schematic view to assist in explaining a method ofmolding a disk-shaped part;

[0018]FIG. 5 is a schematic view to assist in explaining a method ofmolding a cylindrical part;

[0019]FIG. 6 is a sectional view taken on line A-A in FIG. 1;

[0020]FIG. 7 is a graph showing the relation between the depth ofgrooves and linear expansion coefficient in the throttle valve accordingto the first embodiment;

[0021]FIG. 8 is a graph showing the relation between the depth of agroove and gap in the throttle valve in the first embodiment;

[0022]FIG. 9 is a schematic diagram showing a throttle valve in amodification of the first embodiment;

[0023]FIG. 10 is a sectional view of another throttle valve according tothe first embodiment, taken on line A-A in FIG. 9;

[0024]FIG. 11 is a typical view of a throttle valve in a secondembodiment according to the present invention;

[0025]FIG. 12 is a sectional view of a mold for molding the throttlevalve in the second embodiment;

[0026]FIG. 13 is a perspective view of an analytic model of a throttlebody;

[0027]FIG. 14 is a top view of the analytic model shown in FIG. 13;

[0028]FIG. 15 is a fragmentary perspective view of a throttle body in afourth embodiment according to the present invention;

[0029]FIG. 16 is a top view of the throttle body shown in FIG. 15;

[0030]FIG. 17 is a fragmentary top view of the throttle body in thefourth embodiment;

[0031]FIG. 18 is a fragmentary top view of the throttle body in thefourth embodiment;

[0032]FIG. 19 is a fragmentary top view of the throttle body in thefourth embodiment;

[0033]FIG. 20 is a view of to assist in explaining a deformation mode ofthe throttle body in the fourth embodiment;

[0034]FIG. 21 is another example of a section on line A-A in FIG. 9; and

[0035]FIG. 22 is a table showing measured coefficients of linearexpansion.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Preferred embodiments of the present invention will be describedhereinafter with reference to the accompanying drawings. Referring toFIGS. 2 and 3, a throttle body 3 has a throttle valve 1 contained in aspace surrounded by a bore wall 4 a of a bore 4, and a throttle shaft 5.The throttle valve 1 is fastened to the throttle shaft 5 with screws 22.Throttle shaft 5 is extended substantially diametrically across bore 4.A throttle lever 7 is connected to one end of the throttle shaft 5. Areturn spring 6 is extended between throttle lever 7 and a stopper 8. Athrottle-valve position sensor 9 is attached to the other end ofthrottle shaft 5.

[0037] When the driver depresses an accelerator pedal, not shown,throttle lever 7 is moved and throttle shaft 5 is moved accordingly toopen throttle valve 1. When the force applied to the accelerator pedalis removed, throttle valve 1 is closed by the resilience of returnspring 6. In a state where throttle valve I is closed, the gap betweencircumference I a of throttle valve 1 and bore wall 4 a is, for example,in the range of 80 to 100 μm to reduce idle speed, fuel consumption andnoise during idling. This gap enables the smooth movement of throttlevalve 1. In FIG. 3, the gap is exaggerated to facilitate understanding.

[0038] When throttle body 3 is heated by the heat generated by theengine, part of the gap between circumference 1 a of the throttle valveand bore wall 4 a decreases, and the throttle valve 1 bites into thebore wall. This phenomenon is liable to occur mostly during idling.

[0039] The linear expansion coefficient of a resin containing a fibrousfiller in a direction parallel to the extending direction of the filleris small, and that of the same in a direction perpendicular to theextending direction of the filler is large. FIG. 4 is a schematic viewof assistance in explaining a method of molding a common disk, in whicha filler is indicated at 10, a disk is indicated at 11 and a runner isindicated at 12. A resin flows through runner 12 to a positioncorresponding to the center of disk-shaped part 11. As shown in FIG. 4,filler 10 is oriented radially from the center when the thickness ofdisk-shaped part 11 is small. Filler 10 is enlarged in FIG. 4 tofacilitate recognizing the direction of orientation. Therefore, it isexpected that radial thermal deformation is smaller than circumferentialthermal deformation. FIG. 5 is a schematic view of assistance inexplaining a method of molding a cylindrical part. Gates symmetricalwith respect to a circumferential direction are formed to improveroundness. Shown in FIG. 5 are a cylindrical part 13, a gate 14 and arunner b 15. In this case, filler 10 extends in a flowing direction andis generally axially oriented. It is expected that circumferential andradial coefficients of thermal deformation are large, an axial thermaldeformation is small. FIG. 22 shows measured coefficients of linearexpansion of a cylindrical part and a disk-shaped part made of a resincontaining filler 10.

[0040] The circumferential linear expansion coefficient of thecylindrical part is 1.6 times the axial linear expansion coefficient ofthe same, and the circumferential linear expansion coefficient of thedisk-shaped part is 1.4 times the radial linear expansion coefficient ofthe same, which substantiates the aforesaid expectation. Suppose thatthe cylindrical part is a bore, and the disk-shaped part is a throttlevalve. Then, the circumferential linear expansion coefficient of thecylindrical part, and the radial linear expansion coefficient of thedisk-shaped part are related with the gap. There is a large differencebetween the circumferential linear expansion coefficient of thecylindrical part of 28.8×10⁻⁶/° C. and the radial linear expansioncoefficient of the disk-shaped part of 1 8.8×10⁻⁶° C. When the insidediameter is 60 mm, a difference between sizes in the working temperaturerange of −40 to 120° C. is 96 μm. Thus, it is important to make thecoefficients of linear expansion the same in both parts. In this case,the difference between the respective deformations of the bore and thethrottle vale must be smaller than 80 μm. The deformation difference of80 μm corresponds to a difference of about 8×10⁻⁶/° C. in linearexpansion coefficient when the inside diameter is 60 mm and the workingtemperature range is −40 to 120° C. Thus, to prevent galling of the boreand throttle valve, the difference between the respective coefficientsof linear expansion of both parts must not be greater than about8×10⁻⁶/° C. More preferably, in view of changes in roundness, it isdesirable that the deformation difference is 40 μm or below.

[0041] In this embodiment, a method of increasing the radial linearexpansion coefficient of throttle valve 1, which is easier to deal withthan the throttle body 3, has been devised. Preferred embodiments of thepresent invention will be described with reference to the accompanyingdrawings.

[0042] First Embodiment

[0043]FIG. 1 is a typical view of a throttle valve 1 in a firstembodiment according to the present invention. Shown in FIG. 1 are athrottle valve 16, some of grooves 17 arranged on concentric circles,and holes 24 for attaching throttle valve 16 to a shaft 5. FIG. 6 is asectional view taken on line A-A in FIG. 1. A filler may also be added,and oriented.

[0044] Filler 2 can be oriented mostly in a circumferential direction byarranging grooves 17 on concentric circles. Grooves 17 are in a zigzagarrangement in this embodiment to make a resin flow through thin partsof each groove without fail. Thus, the radial flow of the resin isdisturbed to make the extension of the filler in radial directionsdifficult, and the probability of the filler extending in acircumferential direction increase. [00441 The filler can be morerandomly oriented by changing the depth, size and pitches of grooves 17.When the filler is oriented mostly in a circumferential direction, it isdesirable that the linear expansion coefficient of throttle valve 1 isclose to that of bore 4.

[0045] The difference in the linear expansion coefficient betweenthrottle valve 1 and bore 4 can be made smaller than that when thefiller is radially oriented in the throttle valve by randomly orientingthe filler, which is within the scope of the present invention.

[0046] Consequently, as mentioned above, the radial linear expansioncoefficient of the throttle valve can be made to approach that of bore 4to suppress the variation of the gap between throttle valve 16 and bore4 according to temperature variation. Throttle valve 16 in thisembodiment can be easily made by injecting a thermoplastic resin into acavity of a mold provided with protrusions corresponding to the grooves.

[0047]FIG. 7 shows the coefficients α of linear expansion of four typesof disk-shaped parts of a thickness of t₀=3 mm and an outside diameterof 60 mm, respectively provided with grooves of depths of 0.5 mm, 0.75mm. and 1.0 mm. Minimum thicknesses t of the disk-shaped parts, whichare associated with these depths of the grooves, are 2.0 mm, 1.5 mm. and1.0 mm, respectively. The thickness ratio t/t₀ is measured on thehorizontal axis, and the linear expansion coefficient ratio α/α₀, i.e.,the ratio of the linear expansion coefficient a of the throttle valve tothe linear expansion coefficient α₀ of the bores is measured on thevertical axis. The effect of the grooves is significant and the linearexpansion coefficient ratio α/α₀ approaches 1 when the thickness ratiot/t₀ is smaller than ⅔; that is, the respective linear expansioncoefficients of the disk-shaped part and the bore approach each other.

[0048]FIG. 8 shows calculated gap information between the disk-shapedpart and the bore in the temperature range of −40 to 120° C. The gap is49 μm when the disk-shaped part is not provided with any grooves. Thegap is as small as 18 μm when the disk-shaped part is provided withgrooves of 1 mm in depth. In this embodiment, the gap can be limited to40 μm or below (0 to 40 λm) when the temperature of the disk-shaped partis in the temperature range of −40 to 120° C. by forming grooves in thedisk-shaped part such that the minimum thickness is ½ of the originalthickness or below. This corresponds to a linear expansion coefficientdifference of about 4×10⁻⁶/° C. 0 to (4×10⁻⁶/° C.) when the insidediameter is 60 mm.

[0049] The linear expansion coefficient α of 23.7×10⁻⁶/° C. of thedisk-shaped part in this embodiment is greater than the linear expansioncoefficient of 18.1×10⁻⁶/° C. of a disk-shaped part shown in FIG. 22 andis near the linear expansion coefficient of 28.8×10⁻⁶/° C. of the bore.It is inferred that this is the result of the increase of a part notsubject to the influence of shearing with a wall surface resulting froman increased thickness in the range of 1.5 to 3.0 mm and increased ratioof circumferentially oriented fibers.

[0050] Referring again to FIG. 1,] to prevent galling of the throttlevalve and bore 4, practical throttle valve 16 is in contact with bore 4in a position inclined at several degrees to the axis of the bore andnot perpendicular to the axis of the bore. Therefore, practical throttlevalve 16 is not a perfectly circular disk, but an elliptic plate that istapered. The mold is made to conform to the shape of throttle valve 16.

[0051] Although grooves 17 are formed in the opposite surfaces, grooves17 may be formed in only one of the opposite surfaces for the sameeffect. However, when grooves 17 are formed in only one of the oppositesurfaces, measures to prevent the warp of the throttle valve, such asheating different parts of the mold at different temperatures,respectively, must be taken. Although grooves 17 are in a zigzagarrangement in this embodiment, the grooves may be radially arranged.The throttle valve may be provided with concentric circular grooves.Grooves 17 may be formed only in a peripheral part for the same effect.

[0052] Throttle valve 1 is bent around the throttle shaft by a negativepressure during idling. As mentioned above, since throttle valve 11 isnot perpendicular to the axis of the bore and is inclined at an angle tothe axis of the bore, the half of the throttle valve closer to theengine is bent so as to recede from the bore wall. The other half of thethrottle valve farther from the engine is bent to come into the borewall. Consequently, the throttle valve and the bore gall and there isthe possibility, in the worst case, that the throttle valve will becomeuncontrollable.

[0053] As shown in FIG. 9, ribs are formed on the half of the throttlevalve farther from the engine (right half in FIG. 9) instead of thegrooves so that the filler is circumferentially oriented. FIG. 10 showsgrooves 17 and ribs 23. Thus, the reduction of the thickness due to theformation of the grooves is avoided and the rigidity of this half isincreased. FIG. 10 is a sectional view taken on line A-A of FIG. 9. Mostof filler 10 is circumferentially oriented in the half of the throttlevalve provided with ribs 23 shown in FIG. 10. Therefore, the linearexpansion coefficient of throttle valve 1 can be made near orsubstantially equal to that of the bore. Consequently, the strength ofthrottle valve 1 can be increased and, at the same time, the differencein the linear expansion coefficient between the throttle valve and thebore can be reduced to a value not greater than the predetermined value,which can solve the problem with galling of throttle valve 1 and bore 4.

[0054] The ribs may be formed on either one or both of the oppositesurfaces. If the ribs are formed on only one of the surfaces, flowresistance can be reduced by forming protrusions on the side of theengine. FIG. 21 shows another section of a throttle valve correspondingto the section taken on line A-A of FIG. 9. FIG. 21 shows grooves 17 andribs 23. The ribs are formed in the right half of the throttle valvesuch that the height of the rib nearer to the circumference is greaterthan that of the rib farther from the circumference to enhance thebending rigidity of the rib. The adhesion of carbon and oils to aperipheral part 30 can be avoided without forming any ribs in peripheralpart 30.

[0055] Possible filler materials for the resin used in this embodimentare, for example, glass fibers, carbon fibers, boron fibers, aramidfibers, carbon silicate fibers, alumina fibers and potassium titanate(K_(n)O•nTiO₂) whiskers.

[0056] Second Embodiment

[0057]FIG. 11 is a typical view of throttle valve 1 to assist inexplaining a method of manufacture in a second embodiment according tothe present invention. FIG. 12 is a sectional view of a mold used inmanufacturing throttle valve 1. There are shown an aggregate 18 formedby circumferentially arranging filler 18, a lower mold 19, and an uppermold 20. The aggregate of filler is placed in a recess formed in lowermold 19, and a thermosetting resin is poured in the recess to impregnatethe filler with the thermosetting resin. The lower mold 19 and uppermold 20 are joined together, and the mold is heated to set thethermosetting resin. In throttle valve 1 in the second embodiment, thefiller is arranged circumferentially. The linear expansion coefficientof the second embodiment, like that of the first embodiment, can be madeto approach the linear expansion coefficient of bore 4, so that it ispossible to prevent the variation of the gap between throttle valve 1and bore 4 according to the variation of temperature.

[0058] Although the aggregate of filler is used in the secondembodiment, a filling member formed by arranging strings of filler 2 inconcentric circles or in a spiral may be used. Even a filling memberlike a fabric formed by weaving threads of filler is somewhat effective.A throttle valve 1 having the same properties can be manufactured byusing a cold-setting resin, a photocurable resin or a thermoplasticresin instead of the thermosetting resin. If a photocurable resin isused, upper mold 20 must be a glass mold.

[0059] Third Embodiment

[0060] The radial linear expansion coefficient of a throttle valve 1 canbe made to approach the circumferential linear expansion coefficient ofa bore 4 by another method that forms throttle valve 1 with a resinhaving a filler content different from that of a resin forming bore 4.Generally, the linear expansion coefficient of a resin having a smallfiller content is large. The linear expansion coefficient of throttlevalve 1 in this embodiment can be made to approach the circumferentiallinear expansion coefficient of bore 4 by forming throttle valve 1 of aresin having a small filler content. Consequently, the variation of thegap between throttle valve 1 and bore 4 according to the variation oftemperature can be suppressed.

[0061] The radial linear expansion coefficient of the throttle valve canbe made to approach the circumferential linear expansion coefficient ofthe bore by forming the throttle valve and the bore of different resins,respectively.

[0062] Fourth Embodiment

[0063]FIG. 13 shows perspective view of an analytic model to assist inexplaining the postmolding shrinkage that occurs after injection moldingof a throttle body in a fourth embodiment according to the presentinvention. A bore 4, bearing housings 25 for housing bearings supportinga throttle shaft, and through holes 26 through which the throttle shaftis extended are shown. The bore is 50 mm in diameter and 100 mm inheight; the housing is 20 mm in diameter and 10 mm in height; thethrough holes are 10 mm in diameter, and the bore has a wall thicknessof 2 mm.

[0064] Flow, holding and warp during injection molding were analyzedusing this model and general-purpose resin flow analyzing software(MOLDFLOW). A PEI (polyetherimide) containing 25% glass fibers and 20%mica as filler (ULTEM 3452 made by GE Plastics) was used.

[0065]FIG. 14 shows the results of the analysis. Broken lines 27indicate, in an enlarged view, the position of the bore corresponding tothe position of the center of the throttle shaft after shrinkage. Asobvious from FIG. 14, the shrinkage of the part corresponding to thebearing housings 25 is large and the bore 4 has a laterally elongateelliptic shape. To form this part in a shape having a satisfactoryroundness, an annular rib 28 of 2 mm in thickness and 10 mm in width wasformed around a part corresponding to the center of the throttle shaft.FIG. 16 shows the results of analysis performed using the model shown inFIG. 15. Broken lines 29 indicate, in an enlarged view, the position ofthe bore corresponding to the position of the center of the throttleshaft after shrinkage. As obvious from FIG. 16, the shrinkage of thebore is different from that of the bore shown in FIG. 14, and a partcorresponding to the bearing housings and the bore has a longitudinallyelongate elliptic shape. It was inferred that such shrinkage occurredbecause the shrinkage of the annular rib is greater than a partcorresponding to the bearing housings.

[0066] It is known from the foregoing results that the roundness of thebore after shrinkage can be improved by properly determining the shapeof the annular rib. FIG. 17 shows a bore provided with partial ribs. Thepartial ribs narrow the ranges of the shrinking effect of the ribs. FIG.18 shows a rib having a narrow width. FIG. 19 shows ribs having acontinuously changing width. The roundness of the bore can be greatlyimproved by these ribs.

[0067]FIG. 20 is a diagram to assist in explaining the dependence ofdeformation due to postmolding shrinkage on the shape of the rib, inwhich the ratio h/ho, i.e., the ratio of the maximum width h of the ribto the height ho of the boss, is measured on the horizontal axis, andthe ratio hb/h, i.e., the ratio of minimum width hb of the rib to themaximum width h of the rib, is measured on the vertical axis. The boreis deformed in a laterally elongate elliptic shape, in a longitudinallyelongate elliptic shape, and in a nearly square shape when any ribs arenot formed, when a large rib is formed, and when a rib having acomparatively narrow, uniform width is formed, respectively. Theroundness after molding shrinkage is the smallest in the vicinity of theboundaries of those three deformation modes. The roundness is 80 μm orbelow in a range where the maximum width is in the range of 15 to 40% ofthe height of the boss, and the minimum width is in the range of 20 to80% of the maximum width. In FIG. 20, the respective mean wallthicknesses of the rib and the bore are substantially equal. It isconsidered that sinks are dependent not only on the width of the rib andthe height of the boss, but also on the volume. When the rib and theboss differ from each other in wall thickness, the deformation mode willbe similar to the case where the width of the rib and the height of theboss are multiplied by the wall thickness. The same effect as thatobtained when the rib and the boss have the same wall thickness isexpected when the rib is formed such that the product of the maximumwidth and wall thickness of the rib is in the range of 15 to 40% of theproduct of the height and the mean wall thickness of the boss, and theproduct of the minimum width and wall thickness of the rib is in therange of 20 to 80% of the product of the maximum width and wallthickness of the rib.

[0068] Since the throttle valve is inclined at an angle in the range of5° to 7° when closed, the roundness must be 80 μm or below in a range of±5 mm along the center axis of the bore from a position corresponding tothe throttle shaft. The results of the analysis showed that theroundness is substantially 80 μm or below in the aforesaid ranges.Although the rib is formed in one layer at a position corresponding tothe center of the throttle shaft in this embodiment, ribs may be formedin two or more layers at positions around the center of the throttleshaft. Since the rib enhances the rigidity of the bore, the wallthickness of the bore may be reduced.

[0069] The results of the analysis showed that the roundness of a partcorresponding to the throttle shaft is scarcely improved when the rib isformed in axial range other than an axial range corresponding to theboss. Therefore, the rib must be formed in the axial range correspondingto the boss. The concept of the shape of the rib in this embodimentapplies also to a case where a resin and fiber content different fromthose in this embodiment are used.

[0070] Fifth Embodiment

[0071] When an internal combustion engine, not shown, operates, exhaustgas and blowby gas sometimes flow from the internal combustion enginetoward a throttle valve 1. These gases contain carbon and oils. If thegap between a throttle valve 1 and a bore wall 4 a is narrow, the carbonand the oils adhere to and solidify on a peripheral part of throttlevalve 1 facing bore wall 4 a. Consequently, throttle valve I becomesunmovable.

[0072] The adhesion of oils or carbon can be prevented by formingthrottle valve 1 of a resin which prevents the adhesion of oils, carbonsor any adhesive substance containing oils and carbon. More specifically,water repellency can be increased and the adhesion of oils or carbon tothe throttle valve can be prevented by adding a fluorocarbon resin, suchas PTFE (polytetrafluoroethylene resin) to the resin. Formation of aperipheral part of throttle valve 1 of a resin containing a fluorocarbonresin by two-color molding provides a similar effect. Alternatively,coating the surface of throttle valve 1 with a fluorocarbon resinprovides a comparable effect.

[0073] According to the present invention, bore 4 and throttle valve 1are substantially the same in linear expansion coefficient, keeping thegap between bore wall 4 a and circumference 1 a of throttle valve 1uniform, and avoiding the interference between bore 4 and throttle valve1. Also according to the present invention, the roundness of the portionof the bore around the throttle shaft after molding shrinkage can bereduced.

[0074] Thus, the gap between bore wall 4 a and circumference 1 a of thethrottle valve during idling can be limited to a very small value, sothat a high-performance resin throttle body that permits only a smallamount of air leakage can be obtained. Thus, according to the presentinvention, the adhesion of carbon and oils to throttle valve 1 can besuppressed by adding an additive to the resin and, consequently, faultyoperation of throttle valve 1 can be prevented.

What is claimed is:
 1. A throttle body comprising: a throttle shaftextended substantially diametrically across an intake cylinder bore; anda throttle valve fixed to the throttle shaft and contained in the bore;wherein the bore and the throttle valve are made of a resin containingfiller, and the difference between circumferential deformation of thebore and radial deformation of the throttle valve is in the range of 0to 40 82 m at temperatures in the range of −40° C. to 120° C.
 2. Thethrottle body comprising: an intake cylinder bore; and a throttle valve;wherein the throttle valve and the bore are made of resins containingfiller, and the difference between the linear expansion coefficient ofthe throttle valve and that of the bore is in the range of 0 to 4×10⁻⁶/°C.
 3. The throttle body according to claim 1 or 2, wherein the fillersin the bore and the throttle valve are oriented in substantially thesame direction.
 4. The throttle body according to claim 1 or 2, whereinthe fillers are randomly oriented in the bore and the throttle valve. 5.The throttle body according to claim 1 or 2, wherein the throttle valveis provided with circumferential grooves or ribs, and the filler issubstantially circumferentially oriented in the throttle valve.
 6. Thethrottle body according to claim 1 or 2, wherein the throttle valve isformed by sandwiching an aggregate formed by circumferentially arrangingthe filler between resin layers.
 7. The throttle valve according toclaim 1 or 2, wherein the throttle valve is made of a resin different infiller content from that forming the bore to make the radial linearexpansion coefficient of the throttle valve nearly equal to thecircumferential linear expansion coefficient of the bore.
 8. Thethrottle body according to claim 1 or 2, wherein at least a peripheralpart of the throttle valve facing the bore wall of the bore is made of aresin containing a fluorocarbon resin or is coated with a fluorocarbonresin.
 9. The throttle body according to claim 1 or 2, wherein, aminimum thickness is ⅔ of a maximum thickness or below in the throttlevalve stated in claim
 5. 10. A throttle body comprising: a throttleshaft extended substantially diametrically across an intake cylinder(bore); and a throttle valve fixed to the throttle shaft and containedin the bore; wherein the bore is made of a resin, and an annular rib ofa fixed or continuously changing width, or parts of such an annular ribare formed in a part, corresponding to the throttle shaft, of the boreto counterbalance the effect of sinks due to bosses.
 11. The throttlebody according to claim 9, wherein ribs are formed in parts of the boreprovided with bosses, around the throttle shaft such that the product ofmaximum height and thickness is in the range of 15 to 40% of the heightand the mean thickness of the bosses, and the product of minimum heightand thickness is in the range of 20 to 80% of the product of maximumheight and thickness.
 12. The throttle body according to claim 9,wherein a rib having a maximum width in the range of 15 to 40% of theheight of the bosses and a minimum width in the range of 20 to 80% ofthe maximum width is formed in a part of the bore provided with thebosses, corresponding to the throttle shaft.
 13. The throttle bodyaccording to any one of claims 9, 11 and 12, wherein the bore isprovided in a part thereof with a rib capable of limiting the roundness(diameter) of a part of the bore in the range of ±5 mm along the centeraxis of the bore from a position corresponding to the throttle shaft to80 μm or below.